Southern resident orcas, known for their distinct toothy grins and black-and-white marbled body, are lately sporting large, gray patches and other types of discoloration with skin lesions. And, they appear to be spreading among the population, say concerned scientists in  a recent study published in PLOS ONE. 

Researchers often use skin disease as an indicator of health among marine species, which is why they need to know what the cause is of these mysterious patches on the killer whales. 

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What are the Skin Lesions?

Biologists spotted the increase in gray patches and other discolorations on the whale’s skin in photos taken of 18,697 different whale sightings between 2004 through 2016. 

The team ruled out environmental events that may be causing the infection, like, changes in water temperature, and salinity. They instead suspect the discolored patches are from an infection and that the increase in these lesions may be a sign that the whale pod’s immune system defenses may be decreasing. 

“Before we looked at the data, we had no idea that the prevalence of these skin lesions were increasing so dramatically,” says wildlife veterinarian and study author Joseph K. Gaydos in a statement. “It’s worrisome. Now we need to try and isolate the potential infectious agent.” 

An Endangered Species

Southern resident killer whales are found in the Salish Sea, an inland sea that borders Vancouver, British Columbia, and Seattle, Washington, where they feast on Chinook salmon. The whales roam the waters from Alaska to California and were listed as endangered under the Endangered Species Act in 2005. The population in the Salish Sea consists of three pods called J, K and L. 

When the whales were first counted in 1974, there were 74 individuals. Those numbers increased to 97 individuals in 1997 before plummeting again in 2001 with 79 individuals. Their current population numbers are less than 75 individuals.

The greatest threat to these mammals is contaminants that accumulate in the fish that they eat and those that drain into the oceans. Other factors include vessel traffic, noise and limited food availability.

Peering Into the Secret Life of Whales

Since 1976, researchers at the Center for Whale Research have been photographing the whales to identify individuals and keep population counts. Upon reviewing some images, the biologists began to spot the unusual skin lesions and noticed that some lasted only for a short time. Others were persistent and lasted longer.  

But the changes in skin color were not characterized or specifically tracked over time until now. The photographic evidence is a non-invasive study of skin disorders, especially when capture-release health assessments are impossible. 

After a full review of the images, the team identified six skin lesions, including one called erosions. Erosions are a loss of skin layers, causing skin depression or dimpling along the skin. None of the diseases cause mortality, but the increase in two types of lesions surprised researchers.

Understanding what is causing the skin disease or how it may affect the whale’s long-term is crucial for the endangered species population recovery. Out of 141 whales that were part of the population at some point, 99 percent were photographed with skin lesions. Overall, the find highlights the need for continued monitoring and research to understand the type of skin diseases these whales face.

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